Relative Navigation System and a Method Thereof

ABSTRACT

A method of providing a relative navigation system by projecting into space from a first object a grid that is repeatedly detected from a second object having a second relative reference frame associated with a second origin point on the second object and using range and attitude between the objects to adjust the attitude or range of at least one of the first and second objects.

BACKGROUND OF THE INVENTION

This invention relates generally to the field of relative navigationsystems and methods of relative navigation.

Relative navigation systems are useful for various applications such asautonomous vehicle navigation, mid-air refueling, and space docking. Insome applications, only the range between two objects is required. Inother applications, both the range and the relative attitude (pitch,yaw, and roll) between two objects are required. Such information istypically gathered as a time series and used to make course correctionsin one or more of the objects to enable a desired maneuver or finalrelative position.

Some applications benefit from a minimal form factor and weight, as wellas, highly reliable operation often in harsh environments of a relativenavigation system.

Capture and servicing a space satellite is an example of an applicationwhere a relative navigation system can be used. In such application,both the range and the attitude measurements between the targetsatellite and the chase vehicle are required to allow proper orientationduring capture. Additionally, this application is in an extremeenvironment and excess weight and volume of the satellite or chasevehicle can add to the cost of such operations.

Another application may be autonomous vehicle navigation in a warehouseor factory environment. In such an application high reliability and lowcost are desirable.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a method of providing a relative navigation system byprojecting into space from a first object a grid comprised of aplurality of intersecting lines that define a first relative referenceframe associated with a first origin point on the first object isdisclosed. The grid of a plurality of intersecting lines is repeatedlydetected from a second object having a second relative reference frameassociated with a second origin point on the second object. Theintersecting lines projected from the first object each carry a uniquemodulated signal indicating location within the grid of a plurality ofintersecting lines. The range between the second object and the firstobject is repeatedly determined based on the grid of intersecting linesforming the first relative reference frame. The relative attitudebetween the first and second relative reference frames is repeatedlydetermined over time to form a plurality of relative attitudes.Adjusting at the attitude or range of at least one of the first andsecond objects based on the determined range and relative attitudemeasured.

BRIEF DESCRIPTION OF THE DRAWING

In the drawings:

FIG. 1 is a schematic illustration of first and second objects, eachhaving their own relative reference frame, and capable of navigationaccording to an embodiment of the invention.

FIG. 2 is a schematic view of the relative navigation system accordingto an embodiment of the invention.

FIG. 3 is a view of a grid projected into space from the grid generatorfor use with the navigation system of FIG. 2.

FIG. 4 is a view of several horizontally scanned lines that comprise theprojected grid generated by the grid generator of FIG. 3.

FIG. 5 is a view of several vertically scanned lines that comprise theprojected grid generated by the grid generator of FIG. 3.

FIG. 6 is a representation of one embodiment of the modulation of thescanned lines for use in the grid of FIG. 3.

FIG. 7 is a schematic view of the grid projected into space and thelocation of the detector modules within the grid.

FIG. 8 is a schematic view of a projected beam scanned over the detectormodule field of detection.

FIG. 9 is a schematic of unit vectors from the reference frame of thesecond object to each of the detector modules on the first object.

FIG. 10 is a schematic demonstrating the operation of the relativenavigation system according to one embodiment of the invention.

FIG. 11 is a schematic view of another embodiment of a relativenavigation system where one of the two objects is immobile.

FIG. 12 is a schematic view of yet another embodiment of a relativenavigation system with multiple grid generator devices.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is related to methods and apparatus fordetermining the range and relative attitude of two objects. Thisrelative navigation system has various applications including automatedvehicle navigation, mid-air refueling, space vehicle docking, and spacesatellite capture and servicing.

The invention will initially be described in the context of two dockingobjects 110 and 120, which are schematically illustrated in FIG. 1. Theembodiment of FIG. 1 may be analogized to a mid-air refueling scenario,a space vehicle docking scenario, and a space satellite capture andservicing scenario. In all three of these scenarios, both objects aremoving. However, either one of the objects 110 and 120 could be fixed ornon-moving, with the other of the objects 110 and 120 moving, such as inan automated vehicle navigation, e.g. an airplane landing at an airportor a vehicle moving within a warehouse. It is also possible for theobjects 110 and 120 to both be moving, and the relative navigationsystem may be used to maintain a desired attitude between the twoobjects without the two objects being docked, mated, coupled, etc., asthe case may be. The docking scenario is selected because it is believedto provide the most detailed description.

The first object 110 has a first coordinate system 114 based on a firstorigin 112, within the body. Similarly, the second object 120 has asecond coordinate system 124 based on a second origin 122. The locationof the origins 112 and 122 may be at any desired location within thecorresponding object and need not be coincident with a center of gravityor center of geometry of the object 112 and 122. However, in many cases,it is beneficial to locate the origin at either the center of gravity orthe center of geometry. It is beneficial to select a known originbecause then any location on the body can be determined relative to aknown origin.

Each of the objects 110, 120 have corresponding surfaces 118, 128respectively, which mate when the objects are docked. Therefore, therelative navigation between the objects 110, 120 requires that theobjects be oriented facing each other and then brought into contact. Insuch a docking operation, it is useful to determine both the range andthe time rate of change of the range between the first object 110 andthe second object 120. The range is illustrated as the distance betweenthe first origin 112 of the first object and the second origin 122 ofthe second object, shown as R₁. However, the range could be the distancebetween any other two points, which can easily be determined by relativereference to the distance between the origins 112, 122.

Additionally, the relative attitude and preferably the relative attituderate between the first object 110 and the second 120 must be determined.The attitude is the pitch, yaw and roll of an object relative to areference frame, which may be either of the reference frames 112, 122,for example. The relative attitude information is required to change theorientation of either the first object 110 or the second object 120, orboth, such that the first front surface 118 of the first object 110 iscorrectly aligned with the second front surface 128 of the second object120 as the two objects 110 and 120 approach each other for docking.

In one embodiment, the range and the relative attitude between the firstobject 110 and the second object 120 may be continuously determined overtime, such as with time series data, with some periodicity. One or bothof the objects 110, 120 may apply course corrections and/or attitudecorrections by way of navigation of one or both of the first and secondobjects 110 and 120 to ensure proper mating with the correctorientation.

The manner in which the course correction and/or attitude correctionsare made are not germane to the invention and will be dependent on thetype of vehicle that the objects 110, 120 represent. Any suitable coursecorrector may be used. For example, where the object 110 is a spacestation moving in space and the object 120 is a space vehicle, such as aspace shuttle, docking with the space station, the object 120 will havevarious rockets and thrusters for navigation, which may be used asnecessary to adjust the attitude of the space vehicle to the spacestation for docking. In the case of an airplane landing on a runway, theengines and control surfaces of the airplane will provide thecourse/attitude correction during navigation.

FIG. 2 represents one embodiment of the present invention to determinethe range and the relative attitude of the two objects (not shown here).The embodiment comprises a grid generator 140 and a detector arraycomprised of detector modules 150, 152, 154, and 156. The grid generator140 projects a grid, such as a plurality of intersecting lines, intospace within a field of transmission 141. For convenience, the field oftransmission 141 originates from the second object at the origin 122 ofthe reference frame 124. However, the field of transmission 141 couldeasily originate from a known location spaced from the origin 122.

The detector array comprises multiple detector modules for detecting thegrid generated by the grid generator 140. In this embodiment, fourdetector modules 150, 152, 154, and 156 are carried by the first object110 at some known position 160, 162, 164, and 166 respectively, from theorigin of the first object 114. As illustrated in FIG. 2, all of thedetector modules are in a non-collinear distribution. In otherembodiments, it is contemplated that at least one of the detectormodules is positioned in a non-coplanar distribution to the otherdetector modules. The detector modules may also be both non-collinearand non-coplanar, which will provide the most accurate mathematicalresults.

The detector modules 150, 152, 154, and 156 further have a field ofdetection 151, 153, 155, and 157 respectively. For relative navigationbetween the objects 110, 120, it is presumed that the field of detection151, 153, 155, and 157 of at least one of the multiple detector modules150, 152, 154, and 156 lie within the field of transmission of the gridgenerator 140, enabling at least one of the detectors to “see” the grid.For best performance, the field of detection 151, 153, 155, and 157 ofall of the detector modules 150, 152, 154, and 156 lie within the fieldof transmission of the grid generator 140.

FIG. 3 shows the grid as projected into space from the grid generator140 with a field of transmission 141. As illustrated, the projected gridcomprises intersecting lines. At some distance away from the gridgenerator 140, these intersecting lines are observed as a grid in space,with the size of the grid increasing away from the grid generator 140.

For description purposes, the grid generator can be thought of asprojecting intersecting lines substantially in the y direction of thecoordinate system. If one were to observe the projection of intersectinglines in the x-z plane at some distance R₂ away from the grid generator140, one would observe at first grid 170. If one were to observe thesame projection of intersecting lines at a distance R₃, which is greaterthan the first distance R₂ in the x-z plane, one would observe a secondgrid 190, which appears relatively larger than the grid 170.

The first grid 170 at distance R₂ away from the grid generator 140 isspatially bound in the horizontal direction by a first vertical line 172and a second vertical line 173. There exists a plurality of verticallines spatially and temporally generated in between the first verticalline 172 and the second vertical line 173. The first grid 170 at adistance R₂ away from the grid generator 140 is spatially bound in thevertical direction by a first horizontal line 174 and a secondhorizontal line 175. There exists a plurality of horizontal linesspatially and temporally between the first horizontal line 174 and thesecond horizontal line 175.

The distance R₂ can be any distance between the grid and the gridgenerator. For convenience, the distance is determined between a point176 on the first grid 170 and the grid generator as shown.

The vertical and horizontal lines may be formed in any suitable mannerby the grid generator 140. For example, all of the lines may be formedsequentially or all at once. Either one of the vertical lines orhorizontal lines may be formed before the other. The grid generator mayalternate between vertical and horizontal lines. When the grid generator140 uses a scanning laser to form the grid, the laser will sequentiallyform all of one of the vertical and horizontal lines, followed by thesequential forming of the other of the vertical and horizontal lines.The rate at which the lines are sequentially formed may be so fast thatfor practical purposes, it is as if all of the grid lines weresimultaneously formed.

The second grid 190 at distance R₃ away from the grid generator 140 isfor all practical purposes the same as the first grid 170, but atfurther distance from the grid generator 140 than the first grid 170.The grid 190 is spatially bound in the horizontal direction by a firstvertical line 192 of the second grid 190 and a second vertical line 193of the second grid 190. There exists a plurality of vertical linesspatially and temporally generated in between the first vertical line192 of the second grid and the second vertical line 193 of the secondgrid. The second grid 190 at a distance R₃ away from the grid generator140 is spatially bound in the vertical direction by a first horizontalline 194 of the second grid 190 and a second horizontal line 195 of thesecond grid 190. There exists a plurality of horizontal lines spatiallyand temporally between the first horizontal line 194 of the second gridand the second horizontal line 195 of the second grid. A point 196 onthe second grid 190 is shown.

The similarity of the grids 170 and 190 becomes apparent in the case ofprojected grid lines, where the grid 190 is formed by the same linesforming the grid 170, except the grid 190 is observed at a furtherdistance from grid generator 140, making the grid 190 appear larger thanthe grid 170. In this sense, the grid 190 is the appearance of the gridlines generated by the grid generator at the distance R₃ whereas thegrid 170 is the appearance of the grid lines at the distance R₂. Thus,as object 110 approaches object 120, the grid seen by the object becomessmaller.

The grids 170 and 190 may be of any number of lines. As illustrated,they are comprised of ten vertical lines by ten horizontal lines. A gridcomprised of a greater number of intersecting lines may result inimproved detection angular resolution for a fixed field of transmission141 and distance from the detector 140 than a grid comprised of a fewernumber of intersecting lines. The grids 170 and 190 are depicted as asquare shape, but this is not a requirement for the methods andapparatus of this invention. The grid can be any shape includingrectangular, oval, or circular. Furthermore, the intersecting lines ofthe grids 170 and 190 are depicted as orthogonal; however, this is not arequirement for the methods and apparatus of the present invention. Theangles between the intersecting lines may be right angles, acute angles,or obtuse angles in different parts of the grid.

Although, examples shown use Cartesian coordinates, any appropriatecoordinate system may be used including polar, cylindrical, or sphericalcoordinate systems for both grid generation and for grid detection. Forexample, to form a grid amenable to polar coordinate representation, aseries of concentric circles and lines radiating out from the center ofthose circles may be projected by the grid generator into space.

The radiation source for the plurality of projected lines may be acoherent or incoherent radiation source. For example, when the radiationsource is a coherent source, it may be a solid state laser that emitsradiation at a wavelength in the near-UV range. Additionally, theradiation intensity may be selected, or attenuated by use of an opticalfilter, to reduce the risk of eye damage.

The grid of intersecting projected lines may be generated by rasterscanning each of the lines or by projecting and scanning an elongatedradiation beam. FIGS. 4 and 5 depict one embodiment of how the gridgenerator 140 generates the vertical and horizontal lines. In thisembodiment, the grid generator 140 raster scans horizontal line 200 inthe direction indicated by arrow 206. The grid generator then steps tothe next line location and raster scans the subsequent horizontal line202, again in the direction of 206. This process is repeated for thenext line 204 and all subsequent lines until all the horizontal linesare scanned. The vertical lines are scanned in a similar manner with afirst vertical line 210 raster scanned in the direction indicated byarrow 216, followed by stepping and repeating the process for the nextvertical lines 212 and 214 and all subsequent vertical lines. Additionalmethods and apparatus for generating the intersecting lines aredescribed in detail in US patent publication 2008/0067290, the contentsof which are incorporated herein by reference in its entirety.

A grid word may be encoded at one or more locations of the grid. By gridword, it is meant that the structure or characteristic of the gridprovides data or information that may be read or detected by thedetector modules. In one embodiment, the projected lines comprising theseries of projected intersecting lines are further encoded with adifferent grid word in different regions of the grid to indicate regionswithin the grid of intersecting lines. One manner of encoding of thegrid word is by modulating the beam in the case of a laser being used toform the grid. The modulation is achieved by changing the intensity ofthe beam and/or blocking the beam with some periodicity.

FIG. 6 illustrates an amplitude modulation scheme to modulate and encodescanned lines with a grid word. The amplitude modulation scheme may beapplied to a single line or to multiple lines forming the grid. In thisembodiment, the period of each bit is time T_(s), with a logical ‘1’ bitrepresented by a beam intensity of A and a logical ‘0’ bit representedby a beam intensity of 0. This embodiment further shows a grid wordcomprised of 18 bits transmitted over a time of 18T_(s). Some of thesebits may be data bits for encoding the location on the grid and otherbits might be grid word start or stop indicators or error checking bits.Thus, as the detector module monitors the amplitude of the line overtime, a processor or circuitry associated with the detector may be usedto determine the word contained in that location of the grid.

Each of the intersecting projected lines could be encoded differently ora grouping of intersecting lines could be encoded similarly.Additionally, the grid word could be comprised of any number of bits,including any number of start or stop bits, data bits, or errorchecking, correction or parity bits. The data bits may encode each ofthe vertical and horizontal lines with a unique sequence of bits. Upondetection of these bits by the detector module and processing by theprocessor, microcontroller, or other circuitry, the location within thegrid can be determined. Any number of known modulation methods could beused for encoding the grid words on to the plurality of intersectingprojecting lines, including but not limited to, amplitude modulation(AM), frequency modulation (FM), quardrature amplitude modulation (QAM),or combinations thereof.

In another embodiment, the modulated projected lines may be used as acommunication link from the object with the grid generator to the objectwith the detector array. This link can be used to send messages otherthan just information on locations within the grid. For example, themodulated grid lines may be used to send messages such as conveyingwhere in the grid the first object may want the second object to park,or to wait for further commands. The link can be used to send limitedamounts of information by time-multiplexing the information in the gridword. This generalizes the grid as a data link.

FIG. 7 illustrates a view of the grid of intersecting projected lines170 from the normal direction bound by vertical lines 172 and 173 andhorizontal lines 174 and 175 with the field of view 151, 153, 155, and157 of each of the detector modules 150, 152, 154, and 156 (as shown inFIG. 2). In this embodiment each of the vertical and horizontal linesare encoded such that each of the regions within the grid, 1 through100, can be identified. The four detector modules are in a non-co-planerconfiguration with a resulting non-co-planer configuration of the fieldof view 151, 153, 155, and 157 of each of the detector modules. Thecircles in FIG. 7 illustrating the field of view are of different sizesbecause the non-coplanar spacing of the detectors will yield a differentarea, which is defined as the intersection of the field of view with thegrid.

Each detector module produces an output signal based upon the line orlines that pass through the field of view of the detectors. The field ofview may be controlled by selecting the aperture for each detector. Itis possible for each detector to have a different field of view. When aword is embedded in the grid, the field of view of the detector must atleast be large enough such that a projected line is within that field ofview long enough to detect the transmission of a complete grid wordassociated with the line intersecting the detector module. Thus, thefield of view of the detector may be several times the size required todetect a complete grid word of a line passing through the field of viewof the detector, to ensure reliable detection.

The output signals of each of the detectors are then demodulated andprocessed to determine the location of the detector within the projectedgrid of intersecting lines. The demodulation may be conducted by aprocessor, field programmable gate array (FPGA), application specificintegrated circuit (ASIC) or similar computer coupled to the detectors.

The embodiment disclosed herein measures range by counting the number ofbit transitions with periodicity T_(S) of the grid word detected at eachdetector module. Alternatively, one could count the number of lines seenby one or more of the detector modules. However, this approach islimited to the angle of view of the detectors whereas by looking at thebit transitions, it is possible to identify the spot on the grid seen bythe detector, which works better when the objects are close enough thateach detector can only see one line. The method also takes into accountthat the number of bit transitions detected will also be affected by therelative attitude of the detector module to the grid generator.

FIG. 8 illustrates one of the detectors with a field of detection andthe portion of the grid that falls within the field of detection. As canbe seen, the grid generator scans the projected line at an angular rateof ω_(s). The angle subtended in one cycle time T_(s) 222 is ω_(s)T_(s).The number of bit transitions detected by the detector module is givenby the following relationship:

$N_{S} = \frac{{Tan}^{- 1}\left( \frac{D_{A}}{R_{A}} \right)}{\omega_{S}T_{S}}$

Where D_(A) is the dimension of the field of detection 151 of detectormodule 150.

N_(S) is the number of bit transitions detected by the detector module.

R_(A) is the distance from the grid generator 140 to the detectormodule.

Solving for R_(A) gives the following relationship:

$R_{A} = \frac{D_{A}}{{Tan}\left( {N_{S}\omega_{S}T_{S}} \right)}$

The position vector to each of the detectors is given by:

$R_{i} = {\begin{bmatrix}u_{x}^{d} \\u_{y}^{d} \\u_{z}^{d}\end{bmatrix}R_{A}}$

Where i indexes each detector and u^(d) _(x), u^(d) _(y), and u^(d) _(z)are the x, y, and z components of the unit vectors in the referenceframe 124 of the second object 120 in the direction of each of thedetectors as shown in FIG. 9. Each of the vectors 132, 134, 136, and 138from the origin 122 of the reference frame 124 of the second object 120is shown. The x, y, and z components of each of these unit vectors foreach of the detectors is represented by u^(d) _(x), u^(d) _(y), andu^(d) _(z), respectively and are derived from grid angle information.

The position vectors from all the detector modules are processed usingan Absolute Orientation algorithm which determines the relative attitudedirection cosine matrix between the coordiante frame defined by the gridgenerator 140 on the second object 120 and the coordinate frame on thechase vehicle in which the vectors to the detector positions is defined.The distance from the second object to each detector i on the firstobject is given by the equation:

R _(i) =C _(B) ^(R) D _(i) +r _(i)

Where C^(R) _(B) is the relative attitude direction cosine matrix;

D_(i) is the distance from the origin 112 of the first object 110 toeach detector module i on the first object 110, and is a fixed andmeasurable quantity that is the scalar length of vectors 160, 162, 164,and 166 between the origin 112 of the first object and each of thedetectors as shown in FIG. 2; and

r_(i) is the distance between grid generator 140 and origin 122 of thecoordinate frame 124 and the origin 112 of the coordinate frame 114 ofthe first object 110.

The method solves for the relative attitude direction cosine matrix,C^(R) _(B) given the grid generator 140 measurements, R_(i) and thefixed distances, D_(i). A minimum of three and preferably fourmeasurement pairs {R, D}_(i) are required for the solution. In oneembodiment, the Horn Algorithm is used to solve the relative attitudedirection cosine matrix; however, any other known methods may be usedfor this solution.

Multiple determinations over time of the direction cosine matrix mayprovide the basis for determining the rate of change in the attitudebetween the first object 110 and the second object 120. At least twodirection cosine matrices must be determined to calculate a rate ofchange. A sampling rate for determining the position data and thecorresponding direction cosine matrix will be selected based on theanticipated environment and rate of change such that the resultingattitude rate change will provide useful data.

In one embodiment the attitude rate can be determined from backdifferencing the relative attitude direction cosine matrix. A timeseries of attitude rates can be determined from the time series ofrelative attitude direction cosine matrices. The particular method forconducting the back differencing is not germane to the invention. Anysuitable method may be used to obtain the attitude rate.

A Kalman Filter may be used to estimate the relative position of theorigin of the first object 112 to the origin of the second object 122,as well as the relative velocity from multiple position observations asdisclosed above. Each orthogonal element of the position measurement maybe processed with a multi-state Kalman filter to estimate the relativeposition, velocity and possibly other parameters such as accelerationbetween the first object 110 and the second object 120. Methods otherthan multi-state Kalman filter may be used to make these calculations.In one embodiment, the algorithms described are executed in a processingunit 142 such as a microprocessor or a microcontroller as shown in FIG.10.

It may be advantageous in certain applications and system designs tohave a greater field of detection of the detector module (D_(A)). In oneembodiment, the detection module may be comprised of a detector of theradiation emitted by the grid generator 140 and one or more opticalelements to enhance the field of detection of the detector module. As anexample the detector may be a silicon based photodetector. The one ormore optical elements of the detector module may comprise mirrors,lenses, or combinations thereof. In another embodiment, the detectormodule does not comprise any optical elements.

The relative range, velocity, attitude, and rate of attitude determinedfrom the apparatus and methods described herein are used for relativenavigation of one or both of the objects 110 and 120. The data may beused for course corrections for purposes of one object approaching theother object, one object approaching the other object at a preferredvelocity, one object approaching the other object at a preferredvelocity and attitude, for the objects to avoid each other or tomaintain a required distance or orientation between the objects.

FIG. 10 shows an example of the two objects 110, a chase vehicle, and120, a target vehicle, orienting and docking with each other with thefront face 118 of the first object 110 approaching the front face 128 ofthe second object 120 using the apparatus and following the methodsdisclosed. The two objects 110 and 120 are initially non-oriented witheach other and at a distance as indicated by position A of the firstobject 110. The grid generator 140 on the second object 120 continuouslyprojects a grid of intersecting lines that is detected by the detectormodules 150, 152, 154, and 156 on the first object 110. The outputs ofthe detectors are communicated to the processing unit 142 by thedetector module communications path 144. The outputs of each of thedetector modules 150, 152, 154, and 156 are demodulated and processed inthe processing unit 142 to determine the range and relative attitudebetween the two objects 110 and 120 using the algorithms and methodsdisclosed above. Based upon the relative attitude and range determined,the processing unit may initiate a course corrector, which isillustrated as the firing of one or more thrusters 146, to change theorientation and position of the first object 110 as shown in position Bat some time after the object 110 was at position A. The processing unitcommunicates with the thrusters via a thruster communication path 148.This process is then repeated, with the detector modules 150, 152, 154,and 156 detecting the grid of intersecting lines projected by the gridgenerator 140 located on the second object 120, with the outputs of thedetector modules processed by the processor unit 142 to determine therelative attitude and range between the two objects 110 and 120, andthen using this information to initiate course corrections by firing oneor more thrusters 146 on the first object 110 to preferentially changethe position and orientation of the first object 110. This process isrepeated until a final position and orientation of the first object 110that allows docking with the second object 120 is achieved as shown inposition D.

As illustrated in this example, there are two intermittent maneuveringoperations shown, however, there may be any number of maneuveringoperations. The number of maneuvering operations may depend on thesampling period of the measurements, initial distance between the twoobjects 110 and 120, or the initial relative attitude of the two objects110 and 120. The grid generator 140 on the second object 120 and thedetectors 150, 152, 154, and 156 and processing unit 142 on the firstobject 110 may be located on their respective objects to not interferewith the maneuvering or docking process and not incur damage during suchoperations. The processing unit 142 may comprise one or more processors,microcontrollers, memory devices, digital signal processors, fieldprogrammable gate arrays, integrated circuits, discrete electroniccomponents, discrete passive components, circuit boards, electricalconnectors, power supplies, or combinations thereof. The detector modulecommunications path 144 and the thruster communications path 148 may beeither a protocol or non-protocol based communications path, and mayemploy any known medium such as twisted pair or coaxial cable, oralternatively communicate wirelessly by any number of known protocolsand standards such as ZigBee or Bluetooth.

The aforementioned methodology can be used in substantially the samemanner for other applications. For example, in an automated airplanelanding on a runway, the processing unit may control airfoils and othercontrol surfaces of the aircraft based on the time series range andattitude data collected, rather than thrusters as in the space dockingapplication.

For illustrative purposes, the relative navigation of two objects isconsidered and disclosed, but the methods and apparatus disclosed may beused for the relative navigation of multiple objects. It is also obviousthat if course corrections are carried out on the object carrying thegrid generator (second object 120) rather than the object carrying thearray of detector modules (first object 110), or if both objects makecourse corrections, then the first object must communicate the range andrelative attitude time series data to the second object. Thiscommunication between the two objects may transpire over a wirelesscommunications channel such as radio frequency communication with theuse of a variety of communications protocols on either a unidirectionalor bi-directional channel. Alternatively, the communications between thetwo objects may transpire indirectly via a third party such as acommunications satellite with the use of a variety of communicationsprotocols and methods.

The methods and apparatus disclosed produce range and attitude data froma single grid generator on one object and a single array of detectormodules on the other object. Two separate hardware setups are notrequired for the range and the attitude. This has the advantage ofsmaller form factors and weight of a complete navigation system, both ofwhich are important in space and aerial applications. In one embodiment,all the components of the grid generator are packaged as a single unit.Additionally, the detector module array may have redundant detectors,such that high reliability can be achieved even if one or more detectormodules fail during operation.

Illustrated in FIG. 11 is another embodiment of the present invention,wherein the second object 320 is not mobile and is fixed in locationwith a grid generator 340 attached thereon. This object 320 could, forexample, be a wall or ceiling of a building. The first object 310 is amoving object with a front side 318, a rear side 316, a coordinate frame314 with an origin 312, and with one or more detector modules attachedthereon. In one embodiment, there are four detector modules 350, 352,354, and 356. There is a field of transmission 341 of the radiation fromthe grid generator 340. This radiation is radiated in a manner togenerate a plurality of projected intersecting lines. These projectedlines are either elongated beam lines scanned in one direction or pointbeams raster scanned in substantially both the horizontal and verticaldirections. In one embodiment the plurality of intersecting lines arefurther modulated to encode them distinctly from other of the pluralityof intersecting lines. The detector modules 350, 352, 354, and 356 onthe first object detect the position on the projected grid generated bythe grid generator 340. The output of the detector modules are processedwith algorithms to generate one or more of relative range, velocity,attitude and rate of attitude between the first object 310 and thesecond object 320 in a repeating time series manner. These measurementsare then used for real time course correction of object 310 to achieveproper range and orientation of the first object 310 to the secondobject 320. It should also be noted that the first object may be movingin a two dimensional plane such as a car on a flat surface or in a threedimensional plane such as an aerial application.

FIG. 12 is another embodiment of the present invention, where there is afirst object 410, with a front surface 418, a rear surface 416, with areference coordinate system 414 with an origin 412 and several detectormodules 450, 452, 454, and 456 attached thereon. The second object 420in this embodiment has a front surface 428 and a rear surface 426 andhas more than one grid generator attached thereon. Grid generators 440,442, 444, and 446 have a field of transmission of 441, 443, 445, and 447respectively. Several grid generators may be desirable in certainapplications to enable navigation over a wider range of relativepositions. In a single grid generator case, if none of the detectormodules of first object are not within the projection of the gridgenerator then it might be difficult to navigate the first object tobring it within the field of projection of the grid generator. Withmultiple grid generators, the relative range, velocity, attitude andattitude rate may be determined in a greater volume of space surroundingthe second object 420. When using multiple grid generators, anadditional complexity of differentiating between the transmissions ofthe various grid generators must be addressed. In one embodiment, eachof the grid generators encode the plurality of intersecting linesuniquely from the other grid generators, for example with a unique gridword for all lines, regardless of the grid generator that produced theline. In another embodiment, each grid generator may emit radiation of adistinguishably different wavelength from the other grid generators andthe detector modules on the first object will be able to ascertain thegrid generator by detecting the wavelength of the radiation. In thislater embodiment, each detector module 450, 452, 454, and 456 maycomprise more than one detector sensitive to the various wavelengthsemitted by the several grid generators 440, 442, 444, and 446 located onthe second object. Alternatively the detector modules may comprise oneor more optical filters to detect different radiative wavelengths frommore than one grid generator.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

1. A method of providing a relative navigation system comprising:projecting into space from a first object a grid comprised of aplurality of grid lines defining a first relative reference frameassociated with a first origin point on the first object; repeatedlydetecting the grid of a plurality of lines from a second object having asecond relative reference frame associated with a second origin point onthe second object; repeatedly determining the range from the secondobject to the first object based on the grid of lines forming the firstrelative reference frame; repeatedly determining over time the relativeattitude between the first and second relative reference frames to forma plurality of relative attitudes; and adjusting at least one of thedetermined attitude and determined range of at least one of the firstand second objects based on the determined range and relative attitude.2. The method of claim 1, wherein at least one of the first and secondobjects is a moving object and the other is a non-moving object.
 3. Themethod of claim 1, wherein both of the first and second objects aremoving objects.
 4. The method of claim 3, wherein one of the first andsecond objects is a target vehicle and the other of the first and secondobjects is a chase vehicle.
 5. The method of claim 1, wherein theprojection of a grid comprises projecting a plurality of intersectinglines into space.
 6. The method of claim 1, wherein the projecting ofgrid lines comprises modulating the lines to carry a grid word comprisedof a number of modulated bits to identify the lines within the projectedgrid by their modulated grid word.
 7. The method of claim 6, whereindetermining the range comprises determining the number of bits visibleby a detector on the second object.
 8. The method of claim 5, whereinthe projecting of the intersecting lines comprises first projecting afirst set of parallel and spaced lines followed by projecting a secondset of parallel and spaced lines, orthogonal to the first set.
 9. Themethod of claim 5, wherein the projecting of the intersecting linescomprises projecting a series of concentric circles having a commoncenter and lines radiating out from the center and intersecting theconcentric circles.
 10. The method of claim 1, wherein the repeateddetecting of the grid comprises repeatedly detecting the grid atmultiple locations on the second object.
 11. The method of claim 10,wherein the multiple locations are not collinear.
 12. The method ofclaim 10, wherein the multiple locations comprise at least 3 locations.13. The method of claim 10, wherein the lines are modulated to carry aunique modulated signal indicating location within the grid of aplurality of modulated lines.
 14. The method of claim 13, wherein thedetection at each of the multiple locations is over a detection arealarge enough to allow the detection of the modulated grid word of atleast one line passing over the detection area.
 15. The method of claim1, wherein determining the range comprises determining the number oflines visible by a detector on the second object.
 16. The method ofclaim 1, wherein determining the relative attitude between the first andsecond relative reference frames comprises determining a directioncosine matrix between the first and second reference frames.
 17. Themethod of claim 1, wherein determining the relative attitude between thefirst and second relative reference frames comprises determiningmultiple direction cosine matrices over time.
 18. The method of claim17, wherein the determining the relative attitude between the first andsecond relative reference frames comprises determining an attitude ratebased on the multiple direction cosine matrices.
 19. The method of claim1, wherein the determining the relative attitude between the first andsecond relative reference frames comprises determining an attitude rateof change based on the plurality of relative attitudes.